1. Field of the Invention
This invention relates to a fluorine-containing elastomer composition and more particularly to a fluorine-containing elastomer compositon capable of producing vulcanized products with good vulcanization properties, especially high tensile strength and elongation.
2. Description of the Prior Art
Owing to useful characteristics at elevated temperatures, such as high heat resistance, high chemical resistance, high oil resistance, high weathering resistance, demands for vulcanized products of fluorine-containing elastomer have been drastically increasing in the form of sealing materials such as gaskets, O-rings, packings etc., hoses, sheets, etc. in the fields of the automobile industry, the oil hydraulic industry, the general machine industry, the aviation industry, etc. In other words, it can be said that the demands for the vulcanized products of fluorine-containing elastomers have become versatile and stringent in addition to a demand for more efficient molding and processing.
Vulcanization of the fluorine-containing elastomer was initially carried out with polyamine-based derivatives such as hexamethylenediamine carbonate and methylenebis-(cyclohexyl)amine carbonate, but these vulcanization systems gave a poor scorching resistance such a poor processing safety and a poor storage stability or the vulcanized products had a poor permanent compression strain. Thereafter, a process for crosslinking the fluorine-containing elastomer with a polyhydroxyaromatic compound in the presence of a vulcanization accelerator and an acid acceptor was proposed as another vulcanization system capable of overcoming the afore-mentioned disadvantages, and has been practically utilized up to now.
The vulcanization accelerators so far proposed for the vulcanization system are quaternary phosphonium salt compounds [Japanese Patent Application Kokai (Laid-open) No. 47-191], quaternary ammonium salt compounds [Japanese Patent Publication No. 52-38072 and Japanese Patent Application Kokai (Laid-open) No. 47-3831], quaternary ammonium salt compounds of 8-alkyl (or 8-aralkyl)-1,8-diazabicyclo[5,4,0]-undec-7-ene [Japanese Patent Publication No. 52-8863] and [Japanese Patent Application Kokai (Laid-open) No. 48-55231], or combinations thereof with such an amount of 1,8-diazabicyclo[5,4,0]-undec-7-ene as substantially not to vulcanize the fluorine-containing elastomer [Japanese Patent Publication No. 57-20333], etc.
However, even with these vulcanization systems, neither tensile strength nor elongation of the vulcanized product reaches the desired satisfactory level yet and also the storage stability of green elastomer compostion is not satisfactory yet.
A vulcanization system containing a vulcanization accelerator of the quaternary ammonium salt compound had a considerable susceptibility to moisture absorption and deliquescence at the storage in addition to the aforementioned disadvantages and thus needed a special consideration for the storing. This not only caused a handling trouble, but also often lowered the vulcanization characteristics and the physical properties of vulcanized products.
The present applicant have been so far made extensive studies on acceleration of the vulcanization rate without deteriorating the scorching resistance and the permanent compression strain of vulcanized products and also on solution of the problems appearing in the so far known vulcanization systems, and previously found that in a vulcanization system using a polyhydroxyaromatic compound as a crosslinking agent in the presence of an acid acceptor, not only good storage stability, processing safety and vulcanization characteristics (vulcanization flowability, vulcanization rate, etc.) as green elastomer composition, but also considerably improved mechanical strength and permanent compression strain of vulcanized product, which had been the problems to be improved in the so far known vulcanization system, could be obtained by using a specific quaternary ammonium salt compound and an N-alkyl-substituted amide compound as vulcanization accelerator components at the same time, or further using such an amount of 1,8-diazabicyclo[5,4,0]-undec-7-ene, 1,5-diazabicyclo[4,3,0]-non-5-ene or 4-dialkylaminopyridine whose an alkyl group has 1 to 4 carbon atoms as to substantially fail to vulcanize the fluorine-containing elastomer together with the said two vulcanization accelerator components, and proposed a vulcanization system based on this finding [Japanese Patent Publication No. 59-46986]. The vulcanization system was found to be effective for improving the dispersibility of the system at the kneading and the shapability at the vulcanization molding.
In the said vulcanization system, a quaternary ammonium salt compound represented by the following general formula [II]: ##STR2## wherein R.sub.1 is an aralkyl group having 7 to 20 carbon atoms, R.sub.2 is a hydrogen atom or a dialkylamino group whose alkyl group has 1 to 4 carbon atoms, and X.sup.- is an anion, was used as the said specific ammonium salt compound. A fluorine-containing elastomer compositon containing the quaternary ammonium salt compound and the N-alkyl-substituted amide compound had no fear at all of moisture absorption and diliquescence during the storage. Furthermore, the said fluorine-containing elastomer composition had good storage stability, processing safety, and vulcanization characteristics, and gave a considerably improved shapability at the vulcanization molding, mechanical strength and permanent compression strain to vulcanized products and also had a higher vulcanization rate without deteriorating the scorching resistance.